Smoke alarms are common in both residential and commercial buildings. However, they merely warn of a fire and do nothing to disconnect electrical power. Many fires are caused by electrical products, either due to failure or inappropriate positioning or use. For example, an electric heater may be covered or knocked over or hard wired items, such as an electric stove, may cause a fire.
If no one is present then no action will probably occur. With electrical items, power will remain supplied until the electrical item is sufficiently damaged that a short circuit of some form occurs, tripping a fuse, circuit breaker (CB) or Residual Current Detector (RCD). However, by this stage a fire will usually have been established and be self fuelling—removing the electrical supply will not help.
In addition, electrical faults are a relatively common occurrence in electrical switch boards. These are typically located outside of a building or in a wiring closet. If the switch board is outside, an internal smoke detector will not detect the smoke generated by a switch board fault. If the switch board is in an internal wiring closet, a fire may be established before sufficient smoke escapes the closet to be detected. Further, whether inside or outside a building, a fire in a switch board can easily penetrate into roof spaces or internal cavities because the electrical wires inherently breach any fire walls or other barriers that impede spread of fire.